| MadSci Network: Physics |
Hi Brian,
Interesting question, especially because there is no simple answer to it. I'll start by explaining why lasers do not have to be polarized, and then we will see how we can get a polarized laser.
Nowadays, there are many different kinds of laser: solid-state lasers, gas lasers and fluid lasers [1]. The general principle is that the lasing medium is brought into a non-thermal state[2], in which matter in a higher energy state is more common than matter with a lower energy state[3]. This is an unstable state. If a photon now goes through this matter, it can cause the excited matter to decay, producing more of the same photons, essentially producing an avalanche. This is called stimulated emission, and it is the backbone of laser operation [4, 5]
In many cases, this avalanche of photons is directed back into the lasing medium to get a high, consistent, cohesive energy density. Only a small part "leaks" out, producing the laser beam [6].Generally, whenever a photon triggers stimulated emission, the photon that is produced would have the same polarization as the original photon. In this way, a laser could produce linearly polarized light. There are however two reasons why reality is not as simple:
For your experiments, you should either obtain lasers that are polarized (I had no trouble finding those) or assessing whether the laser you are using is polarized. Using a polarization filter on the laser may not work. Not only is there a decent risk of burning a hole in the filter, the laser light may shift polarization, leading to an unstable power level after the filter.
Good luck with the experiments,
Bart
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